1. Field of the Invention
The present invention relates to a quartz crystal vibrator, an oscillator and an electronic apparatus.
2. Description of the Related Art
In recent years, various quartz crystal vibrators are utilized in a portable telephone or a portable information terminal apparatus as a time source, a timing source of a control signal and the like. In the quartz crystal vibrators, there is a quartz crystal vibrating plate formed by surrounding a quartz crystal vibrating piece by a frame-like portion, and a hermetically closed vessel constituted by interposing the quartz crystal vibrating plate by a lid member and a base member in a plate-like shape in a thickness direction. The quartz crystal vibrators are fabricated, for example, as follows. That is, a bonding electrode comprising aluminum or the like is formed on an outer face of a wafer for constituting a quartz crystal vibrating plate, and the quartz crystal vibrating plate is interposed by two of wafers for constituting the lid member and the base member. Thereafter, the respective wafers are anodically bonded by applying a predetermined voltage to each of the wafers, successively, cut to constitute the quartz crystal vibrators one by one by a dicing step.
Here, when the bonded wafers are cut, end portions of the bonding electrodes are exposed from side faces of the hermetically closed vessels. The bonding electrode comprises a member having a low corrosion resistance of aluminum or the like and therefore, when the end portion is made to stay to be exposed to outside air, the bonding electrode is corroded. When corrosion is brought about, leakage is brought about, the atmosphere starts to flow into a cavity portion formed inside of the hermetically closed vessel by a small amount and a pressure of the cavity portion is changed. As a result, an oscillation frequency and a resonance resistance value of the quartz crystal vibrator are varied by rectified values or more. Hence, in order to prevent the variations, it is well known to form a fluororesin layer for covering to protect the end portion of the bonding electrode at the side face of the hermetically closed vessel (refer to JP-A-2003-264447).
However, according to the above-described constitution, a strength of the fluororesin layer against an external force is insufficient and therefore, there is a concern of bringing about chipping or the like at the fluororesin layer by some factor. Further, although it is conceivable to form the fluororesin layer to be thick in order to increase the strength, when the fluororesin layer is made to be thick, crack or the like is brought about at the fluororesin layer by a stress produced by expansion, contraction or the like by a change in a temperature of outside air. When such a chipping or crack or the like is brought about, outside air or moisture invades from a clearance of the chipping or the crack and the bonding electrode is corroded.